As is well known, motorized door operators automatically open and close a garage door or the like through a path that is defined by a physical upper limit and a physical lower limit. The physical lower limit is established by the floor upon which the garage door closes. The physical upper limit can be defined by the highest point the door will travel, which can be limited by the operator, the counterbalance system, or the door track system's physical limits. The operator's upper and lower limits are employed to prevent door damage resulting from the operator's attempt to move a door past its physical limits. Under normal operating conditions, the operator's limits may be set to match the door's upper and lower physical limits. However, operator limits are normally set to a point less than the door's physical upper and lower limits.
One known limit system employs pulse counters that set the upper and lower travel of the door by counting the revolutions of an operator's rotating component. These pulse counters are normally coupled to the shaft of the motor and provide a count to a microprocessor. The upper and lower limits are programmed into the microprocessor by the consumer or installer. As the door cycles, the pulse counter updates the count to the microprocessor. Once the proper count is reached, which corresponds to the count of the upper and lower limits programmed by the consumer or installer, the door stops. Unfortunately, pulse counters cannot accurately keep count. External factors such as power transients, electrical motor noise, and radio interference often disrupt the count, allowing the door to over-travel or under-travel. The microprocessor may also lose count if power to the operator is lost or if the consumer manually moves the door while the power is off and the door is placed in a new position that does not match the original count.
Motorized garage door operators often include internal or primary entrapment protection systems designed to monitor door speed and applied force as the door travels in the opening and closing directions. During travel from the open-to-close and from the close-to-open positions, the door maintains a relatively constant speed. However, if the door encounters an obstacle during travel, the speed of the door slows down or stops, depending upon the amount of negative force applied by the obstacle. Systems for detecting such a change in door speed and applied force are commonly referred to as "internal entrapment protection" systems. Once the internal entrapment protection is activated, the door may stop or stop and reverse direction.
Most residential operator systems are closed loop systems, wherein the door is always driven by the operator in both the open-to-close and close-to-open directions. A closed loop system works well with the internal entrapment system, wherein the operator is always connected to the door and exerting a force on the door when the door is in motion unless it is disconnected manually by the consumer. If an obstacle is encountered by the door, the direct connection to the operator allows for feedback to the internal entrapment device, which signals the door to stop or stop and reverse. However, due to the inertia and speed of the door and the tolerances in the door and track system, these internal entrapment systems are very slow to respond, and some time passes after contacting an obstruction before the internal entrapment device is activated, thus allowing the door to over-travel and exert very high forces on an object that is entrapped. As such, known internal entrapment systems, by themselves do not work well, especially when the open/close cycle is remotely actuated. Some systems even incorporate timers that will cause the door to open if the bottom limit is not contacted within 30 seconds from the time the door started to close. In most instances, this length of time is much too long. Further, a closed loop operator system always has the capability of exerting a force greater that the weight of the door.
A known method of internal entrapment protection on a closed loop system uses a pair of springs to balance a lever in a center position and a pair of switches to indicate that the lever is off-center, thereby signaling that an obstruction has been encountered. The lever is coupled to a drive belt or chain and balanced by a pair of springs adjusted to counterbalance the tension on the belt or chain so the lever stays centered. When an obstruction is encountered, the tension on the belt or chain overcomes the tension applied by the springs, thus allowing the lever to shift off-center and contact a switch that generates an obstruction signal. Sensitivity of this system can be adjusted by applying more tension to the centering springs to force the lever to stay centered. This type of internal entrapment systems is slow to respond due to the inertia of the door, the stretch in the drive belt or chain, and the components of the drive system.
Another method of the prior art on closed loop operator internal entrapment systems uses an adjustable clutch mechanism. The clutch is mounted on a drive component and allows slippage of the drive force to occur if an obstruction prevents the door from moving. The amount of slippage can be adjusted in the clutch so that a small amount of resistance to the movement of the door causes the clutch to slip. However, due to aging of the door system and environmental conditions that can change the force required to move the door, these systems are normally adjusted to the highest force condition anticipated by the installer or the consumer. Further, over time the clutch plates can corrode and freeze together, preventing slippage if an obstruction is encountered.
In addition to using the aforementioned pulse counters to set the upper and lower limits of door travel, they may also be used to monitor the speed of the garage door. The optical encoders used for speed monitoring are normally coupled to the shaft of the motor. An interrupter wheel disrupts a path of light from a sender to a receiver. As the interrupter or chopper wheel rotates, the light path is reestablished. These light pulses are then sent to a microprocessor every time the beam is interrupted. Alternatively, magnetic flux sensors function the same except that the chopper wheel is made of a ferromagnetic material and the wheel is shaped much like a gear. When the gear teeth come in close proximity to the sensor, magnetic flux flows from the sender through a gear tooth and back to the receiver. As the wheel rotates, the air gap between the sensor and the wheel increases. Once this gap becomes fully opened, the magnetic flux does not flow to the receiver. As such, a pulse is generated every time magnetic flux is detected by the receiver. Since motor control circuits used for operators do not have automatic speed compensation, the speed is directly proportional to the load. Therefore, the heavier the load, the slower the rotation of the motor. The optical or magnetic encoder counts the number of pulses in a predetermined amount of time. If the motor slows down, the count is less than if the motor had moved at its normal speed. Accordingly, the internal entrapment device triggers as soon as the number of pulses counted falls below a manually set threshold during the predetermined period of time.
From the foregoing discussion it will be appreciated that as a residential garage door travels in the opening and closing directions, the force needed to move the door varies depending upon the door position or how much of the door is in the vertical position. Counterbalance springs are designed to keep the door balanced at all times if the panels or sections of the door are uniform in size and weight. The speed of the door panels as they traverse the transition from horizontal to vertical and from vertical to horizontal can cause variations in the force requirement to move the door. Further, the panels or sections can vary in size and weight by using different height panels together or adding windows or reinforcing members to the panels or sections. In prior-art devices, these variations cannot be compensated for.
To compensate for these variations, a force setting must be employed to overcome the highest force experienced to move the door throughout the distance the door travels. For example, the force to move a door could be as low as 5 to 10 pounds at the initiation of the movement and increase to 35 to 40 pounds at another part of the movement. Therefore, the force setting on the operator must be least 41 pounds to assure the internal entrapment device will not activate. If an obstacle is encountered during the time the door is in the 35 to 40 pound range, it will take only 1 to 6 pounds of force against the object to activate the internal entrapment device. However, if the door is in the 5 to 10 pound range, the door will require up to 31 to 36 pounds of force against the object before the internal entrapment device activates. To exacerbate this condition, the force adjustments on these internal entrapment devices are set by the consumer or the installer to allow the operator to exert several hundred pounds of force before the internal entrapment device will activate. As such, it is common to find garage door operators that can crush automobile hoods and buckle garage door panels before the internal entrapment system is triggered.
Two patents have attempted to address the shortcomings of properly triggering internal entrapment systems. One such patent, U.S. Pat. No. 5,278,480, teaches a microprocessor system that learns the open and closed position limits as well as force sensitivity limits for up and down operation of the door. This patent also discloses that the closed position limit and the sensitivity limits are adaptably adjusted to accommodate changes in conditions to the garage door. Further, this system may "map" motor speed and store this map after each successful closing operation. This map is then compared to the next closing operation so that any variations in the closing speed indicate that an obstruction is present. Although this patent is an improvement over the aforementioned entrapment systems, several drawbacks are apparent. First, the positional location of the door is provided by counting the rotations of the motor with an optical encoder. As discussed previously, optical encoders and magnetic flux pickup sensors are susceptible to interference and the like. This system also requires that a sensitivity setting must be adjusted according to the load applied. As noted previously, out-of-balance conditions may not be fully considered in systems with an encoder. Although each open/close cycle is updated with a sensitivity value, the sensitivity adjustment is set to the lowest motor speed recorded in the previous cycle. Nor does the disclosed system consider an out-of-balance condition or contemplate that different speeds may be encountered at different positional locations of the door during its travel.
Another patent, U.S. Pat. No. 5,218,282, also provides an obstruction detector for stopping the motor when the detected motor speed indicates a motor torque greater than the selected closing torque limit while closing the door. The disclosure also provides for at least stopping the motor when the detected motor speed indicates that motor torque is greater than the selected opening torque limit while opening the door. This disclosure relies on optical counters to detect door position and motor speed during operation of the door. As discussed previously, the positional location of the door cannot be reliably and accurately determined by pulse counter methods.
Co-pending U.S. patent application, U.S. Ser. No. 08/906,529, which is owned by the Assignee of the present application and which is incorporated herein by reference, provides for an internal entrapment system. The disclosure provides a potentiometer coupled to the door to determine its position and a pulse counter that determines an amount of force or motor torque used to open and close the door. Although effective, this system optimally requires temperature sensors to accommodate any impact that temperature changes may have on the motor and pulse-counting sequence.
Another type of system connected to a door is a trolley-type garage door operator that applies an operating force to the garage door. As with the other types of garage door opening systems, the trolley-type operator employs a direct connection of the motorized unit to the door. Unfortunately, the trolley-type operator is not sensitive enough to provide adequate entrapment protection in that the operator is slow to respond when an obstruction is encountered, and secondary entrapment protection is required to achieve adequate protection. Based on the foregoing discussion of internal entrapment system, it will be appreciated that there is a great need for a backup or secondary entrapment system. The secondary or external entrapment system is required in the event the internal or primary entrapment system fails or is slow to respond. Common secondary entrapment systems employ photo cells or edge sensors. These devices may have dead spots in areas that need detection beyond the range of individual sensors. This can be corrected by adding additional sensors to cover the dead spot, but this adds to the cost of the protection system and to the cost of installation. Additionally, these types of sensors require alignment to work properly and can become misaligned during use. These sensors are also affected by moisture and dust on their lenses, preventing proper operation. Some of these devices are pressure-sensitive switches that are mounted on the door or the edges of the opening and will generate a signal if compressed, indicating an obstruction is present between the door and the opening. These switches must extend through or along the perimeter of the opening and will increase in cost proportional to the size of the opening. Further, the materials used to manufacture these devices can vary in hardness with the environmental temperatures changing, creating less sensitive detection in cold weather and sometimes too sensitive in hot weather.
Doors that are directly connected to the motorized unit, such as a garage door and a garage door operator, are not precise units due to the slack in the mechanical drive train and the methods of attaching to the door. Moreover, the guide rails and the mountings can deflect when an obstruction is encountered, delaying or preventing standard sensors from indicating an obstruction. It has been determined that conventional methods of determining the door's operating parameters are too vague to provide adequate entrapment protection without the use of external (or secondary) devices, such as photo cells and edge sensors.
Photo cells require wiring sized to the opening to transmit the signal back to the motor controls or a wireless device that requires a battery. The edge sensors that are attached to the door also require wiring that must be commutated from the movable closure to the motor control. Alternatively, a wireless transmitter may be used. Edge sensors that are attached to the opening must also have provisions to send signals to the motor controls. As will be appreciated, this extensive wiring adds to the cost of installation and is susceptible to damage.